The present invention relates to a discharge nozzle assembly for use in discharging molten metal from a metallurgical vessel, and specifically of the type including means for supplying a processing gas into a delivery channel of a refractory nozzle brick of the assembly.
In a casting tube for pouring ladles or in a tundish in a continuous casting plant, is known to introduce a processing gas, such as an inert gas for the casting of primarily aluminum-killed molten steels, into the delivery channel or discharge passage of a refractory nozzle brick in order to prevent the gradual clogging of the delivery channel as a result of the formation of alumina formed during the casting of such molten steels.
Austrian Patent No. 321,480 discloses a prior art apparatus of this general type wherein there are provided two refractory nozzle brick sleeves enclosing a delivery channel concentrically and consisting of differently gas-permeable refractory materials in communication with an annular chamber connected to a gas inlet pipe. Thus, processing gas makes its way from the casting tube to the metallurgical vessel containing the molten metal via a more strongly gas-permeable outer refractory nozzle brick sleeve, and via the less strongly gas-permeable inner refractory nozzle brick sleeve, to the delivery channel. However, considerable leakage losses occur as a result of the high temperatures to which the parts are subjected during operation, particularly around the delivery channel between the outer nozzle brick sleeve and a metal annular chamber enclosing it on the lower side. These leakage losses also occur at a bolted joint between the annular chamber and the gas inlet pipe. As a result, the effective amount of a gas to be injected cannot be determined accurately, and this therefore results in a relatively high consumption of the expensive gas. Furthermore, it has been found that the conventional funnel-shaped upper end of the delivery channel in conventional arrangements is disadvantageous in that it results in eddy currents and turbulence in the molten metal in such funnel-shaped inlet end, thereby reinforcing the tendency of the occurrence of clogging.